Methods and systems for tracking and guiding sensors and instruments

ABSTRACT

A shared-housing ultrasound transducer and machine-vision camera system is disclosed for registering the transducer&#39;s x, y, z position in space and pitch, yaw, and roll orientation with respect to an object, such as a patient&#39;s body. The position and orientation are correlated with transducer scan data, and scans of the same region of the object are compared in order to reduce ultrasound artifacts and speckles. The system can be extended to interoperative gamma probes or other non-contact sensor probes and medical instruments. Methods are disclosed for computer or remote guiding of a sensor probe or instrument with respect to saved positions and orientations of the sensor probe.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/143,301, filed Apr. 29, 2016, which is a divisional of U.S.application Ser. No. 13/789,143, filed Mar. 7, 2013, which claims thebenefit of U.S. Provisional Application No. 61/699,750, filed Sep. 11,2012, and U.S. Provisional Application No. 61/607,676, filed Mar. 7,2012, all of which are hereby incorporated by reference in theirentireties for all purposes.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

NOT APPLICABLE

BACKGROUND 1. Field of the Invention

Generally, this application relates to position and orientationdetermination devices for surgery and other contexts. Specifically, thisapplication relates to computer vision and ranging tracking systems formedical instruments and sensor probes.

2. Background

Currently, hand-held sensor systems are being used for severalapplications, ranging from environmental surveys of chemical, biologicaland radioactive environments, to medical investigations for diagnostics,disease characterization and intraoperative guiding and imaging. Becausethey are hand-held, they can be immediately positioned and oriented withalmost all of the outstanding flexibility and adaptability of a humanoperator's hands.

In some instances, a user may wish to know exactly how and where asensor system is pointed. Yet, the flexibility and adaptability ofhand-held sensors also can make them difficult to track. Prior artapproaches at spatial registration of sensors and instruments are bulky,cumbersome, expensive, or not practical. There are several examples inwhich sensor systems were outfitted with a Global Positioning System(GPS) antenna, Inertial Navigation Unit (INU), magnetic sensors, oroptical markers.

Unfortunately, GPS only provides coarse, limited spatial resolution anddoes not work reliably when satellite GPS signals are weak. INU systemsdrift over time. Magnetic sensors are generally useful for trackingobjects within a small volume of space, around 0.1 to 1 square meters(m³). In a controlled laboratory environment, magnetic sensors canprovide location resolution of about 1 millimeter (mm) inside volumesaround 0.2 m³ and orientation precision to within a degree. However,when used in realistic applications where metallic objects are present,or when other magnetic fields are generated by adjacent electronicequipment, the position resolution decreases to several centimeterswithin a 0.2 m³ volume. This position resolution is too coarse for manyapplications, including medical diagnostic and medical interventionswhere multiple electronic instruments and metallic objects are used.Optical markers attached to probes require a direct and continuous lineof sight to an external Coordinate Measuring Machine (CMM) camerasystem. Generally, CMM camera systems are bulky, expensive andimpractical for most applications in where hand-held systems are used ordesirable.

U.S. Patent Application No. 2009/0259123 A1 proposes a CMM-type systemfor tracking hand-held sensors and instruments for intraoperativenavigated sentinel lymph node dissection. The system proposed thereinuses external infra-red cameras to track coded infrared reflectivemarkers attached to the hand-held probes or hand-held instruments. Onedrawback of this approach is that a continuous line of sight needs toexist between external cameras placed above a surgery table and all ofthe markers placed on probes, instruments, and samples. The hands, arms,and heads of the surgeons may easily break the line of sight duringsurgery procedures.

U.S. Patent Application No. 2012/0253200 A1 uses an augmentation devicein the form of a bracketed structure to be appended to an existingimaging probe to project a pattern of structured light onto the skin oran organ of a patient to facilitate stereo object recognition.

There is a need for better, less expensive, and more accurate andprecise tracking of hand held sensors and medical instruments.

BRIEF SUMMARY

An ultrasound transducer sharing a housing with a machine-vision camerasystem is disclosed. The integrated camera views an object, such as apatient's body, and determines the ultrasound transducer's x, y, zposition in space and pitch, yaw, and roll orientation with respect tothe object. The position and orientation at a point in time are savedalong with an ultrasound scan at the same point of time in a record fileas a “spatially registered scan.” Multiple spatially registered scans ofthe same region of the body are compared in order to reduce ultrasoundartifacts and speckles, and tissue types and elastomeric properties canbe refined. A three-dimensional (3-D) model of tissue can be shown to auser.

For an object with many curved surfaces, fiducial markers can be affixedto the object or overlaid as a piece-wise flexible tape. The markers canuse two-dimensional coding so that they can be discerned from oneanother.

The 3-D model can be used for telemedicine and stereotaxy. A remote userof the system or a computer can guide a local human operator or roboticdevice to move a medical instrument to a particular point on or within apatient's body. Graphical guiding elements such as directional arrows orvirtual space renderings can be used to guide a local operator.

Other sensor probes besides ultrasound transducers can be used withspatially registered scans, such as radar, terahertz radiationdetectors, intraoperative gamma-ray probes, radiation detectors,radiation dosimeters, and chemical sensors.

Some embodiments of the invention are related to a spatial registrationapparatus that includes a rigid housing assembly, an ultrasoundtransducer having a portion enclosed by the housing, a camera having aportion enclosed by the housing assembly and rigidly connected with theultrasound transducer, and at least one processor operatively coupledwith a memory and the camera, the memory having instructions forexecution by the at least one processor configured to determine aspatial position and orientation of the ultrasound transducer withrespect to an object using an image captured by the camera.

The memory can have instructions for execution by the at least oneprocessor configured to associate scanning data from the ultrasoundtransducer with the spatial position and orientation of the ultrasoundtransducer to create and save a spatially registered scan. The memorycan have instructions for execution by the at least one processorconfigured to reduce an ultrasound artifact or speckle using the savedspatially registered scan and another spatially registered scan. Thememory can have instructions for execution by the at least one processorconfigured to identify a tissue type or elastomeric property using thesaved spatially registered scan and another spatially registered scan.The memory can have instructions for execution by the at least oneprocessor configured to construct a three-dimensional (3-D) model of atissue with respect to the object using the saved spatially registeredscan and another spatially registered scan. The memory can haveinstructions for execution by the at least one processor configured torender a three-dimensional (3-D) structure of the object using the savedspatially registered scan of a first scanning plane and a secondspatially registered scan from a second scanning plane. The camera canbe selected from the group consisting of an optical camera, an infraredcamera, a scanning laser camera, a flash laser camera, a time-of-flightcamera, and a structured light camera.

The apparatus can further include a second camera having a portionwithin the housing, in which the memory includes instructions forexecution by the at least one processor configured to determine thespatial position and orientation of the ultrasound transducer withrespect to the object using images captured by the cameras. One cameracan be a time-of-flight camera while the other camera is anon-time-of-flight camera. An inertial measurement unit (IMU) can besupported by the housing, in which the memory includes instructions forexecution by the at least one processor configured to determine thespatial position and orientation of the ultrasound transducer withrespect to the object using output from the IMU. A display can beoperatively connected with the processor, the display configured forvisualizing a three-dimensional (3-D) representation of the objectcreated or refined from the determined spatial position and orientationand output from the ultrasound transducer.

The housing can include multiple housing shells. The memory can haveinstructions for execution by the at least one processor configured tointerpret movements of interactivity elements to execute a process. Thecamera can be part of a head-mounted tracking and visualization systemhaving a display.

Some embodiments are related to a spatial registration apparatus thatincludes a medical instrument or sensor probe, a camera rigidlyconnected with the medical instrument or sensor probe or with a part ofa body of a human operator, at least one processor operatively coupledwith a memory and the camera, the memory having instructions forexecution by the at least one processor configured to determine acurrent spatial position and orientation of the medical instrument orsensor probe with respect to an object using an image captured by thecamera, and at least one processor operatively coupled with a memory,the memory having instructions for execution by the at least oneprocessor configured to derive visualization data from a saved spatiallyregistered scan having a position and orientation corresponding to thecurrent spatial position and orientation of the medical instrument orsensor probe, and display the visualization data to a user.

The user can be remote from or local to the medical instrument or sensorprobe.

Some embodiments are related to a spatial registration apparatus thatincludes a medical instrument or non-imaging sensor probe, a camerarigidly connected with the medical instrument or non-imaging sensorprobe or connected with a part of a body of a human operator and atleast one processor operatively coupled with a memory and the camera,the memory having instructions for execution by the at least oneprocessor configured to determine a current spatial position andorientation of the medical instrument or non-imaging sensor probe withrespect to an object using an image captured by the camera.

The sensor probe can be selected from the group consisting of a radar, aterahertz radiation detector, an intraoperative gamma-ray probe, aradiation detector, a radiation dosimeter, and a chemical sensor. Thesensor probe can be an intraoperative gamma-ray probe, wherein thememory has instructions for execution by the at least one processorconfigured to store radiation count data from the gamma ray probe withthe current spatial position and orientation of the gamma-ray probe.

The apparatus can include a fiducial marker, the at least one processorconfigured to determine the spatial position and orientation of themedical instrument or sensor probe with respect to the object using animage captured by the camera of the fiducial marker on the object. Thefiducial marker can include binary coding and/or one or more lightemitting diodes (LEDs). The apparatus can include a flexible tape havingat least one fiducial marker, the at least one processor configured todetermine the spatial position and orientation of the medical instrumentor sensor probe with respect to the object using an image captured bythe camera of the at least one fiducial marker of the flexible tape onthe object. In an embodiment, the object can have a curved surface, suchas that of a human body, and the flexible tape is conformed to thecurved surface. Each of the at least one fiducial marker can have arigid substrate, the flexible tape including two or more rigid substratefiducial markers piece-wise rotatable with respect to each other. The atleast one fiducial marker can include multiple fiducial markers, eachfiducial marker having a distinct binary coding from one another.

Some embodiments are related to a method for directing a medicalprocedure. The method includes providing a medical instrument or sensorprobe, providing a camera rigidly attached to the medical instrument orsensor probe or connected with a part of a body of a user, calculating acurrent position and orientation of the medical instrument or sensorprobe with respect to an object using an image captured by the camera,and displaying to a user a location of an item of interest or apreviously saved position and orientation of a sensor probe with respectto the medical instrument or sensor probe using the calculated currentposition and orientation.

The displaying can include a graphical guiding element, such as adirectional arrow. The displaying can include a three-dimensional (3-D)rendering of the item of interest or previously saved position andorientation of a sensor probe with respect to the object. The method canfurther include moving the medical instrument or sensor probe inresponse to the displaying. The user to which the item of interest orpreviously saved position and orientation is displayed can be remotefrom or local to the object.

Some embodiments are related to a spatial registration apparatusincluding a non-optical sensor probe, and a clip interface adapted todetachably and rigidly mate to the sensor probe a portable computingdevice having a camera and at least one processor operatively coupledwith a memory, the memory having instructions for execution by the atleast one processor configured to determine a spatial position andorientation of the sensor probe with respect to an object using an imagecaptured by the camera.

The portable computing device can include a smart phone.

Some embodiments are related to a method for spatial registration ofsensor probe. The method includes applying a flexible tape having atleast one fiducial marker to an object of interest, scanning the objectwith a sensor probe, imaging, using a camera, the at least one fiducialmarker of the flexible tape in order to produce one or more images ofthe at least one fiducial marker, the scanning and imaging conductedsimultaneously, computing a spatial position and orientation of thesensor probe with respect to the object using the one or more images ofthe at least one fiducial marker, and correlating features of the objectdetected by the sensor probe using the computed spatial position andorientation.

The method can include conforming the flexible tape to the curvedsurface. The method can include decoding a binary encoding of a fiducialmarker, the correlating using the decoding. The method can includerendering an image of a three-dimensional (3-D) feature of the objectusing the computed spatial position and orientation. The method caninclude detachably mating a smart phone to the sensor probe, the smartphone having the camera and performing the imaging, computing, andcorrelating.

The method can include conforming the flexible tape to a curved surfaceof the object. The method can also include detachably mating a smartphone to the sensor probe, the smart phone having the camera andperforming the imaging, computing, and correlating.

Some embodiments are related to a spatial registration apparatusincluding an instrument or sensor probe, a fiduciary element attached tothe instrument or sensor probe, a camera mechanically connected to apart of the body of a user, the camera aligned to observe an area wherethe user manipulates the instrument or sensor probe, and at least oneprocessor operatively coupled with a memory and the camera, the memoryhaving instructions for execution by the at least one processorconfigured to determine a spatial position and orientation of theinstrument or sensor probe with respect to an object using an imagecaptured by the camera.

With reference to the remaining portions of the specification, includingthe drawings and claims, one of ordinary skill in the art will realizeother features and advantages of the present invention. Further featuresand advantages of the present invention, as well as the structure andoperation of various embodiments of the present invention, are describedin detail below with respect to the accompanying drawings. In thedrawings, like reference numbers indicate identical or functionallysimilar elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates tracking and spatial registration of a medicalinstrument or sensor probe using a ranging device mechanicallyregistered to a probe in accordance with an embodiment.

FIG. 2 is a flowchart of data processing steps using a generic rangingand tracking system mechanically registered to the probe in accordancewith an embodiment.

FIG. 3 . illustrates tracking and spatial registration of probes withrespect to an investigated environment using various optical methods inaccordance with an embodiment.

FIG. 4A illustrates an example fiducial object in accordance with anembodiment.

FIG. 4B illustrates an alternative fiducial object in accordance with anembodiment.

FIG. 5 illustrates a tape-like piece-wise rigid fiducial object inaccordance with an embodiment.

FIG. 6 is a flowchart of data processing steps using a generic machinevision system mechanically registered to the probe in accordance with anembodiment.

FIG. 7 illustrates tracking and spatial registration of a probe inrespect to an investigated environment using an electromagnetic rangingsystem mechanically registered to the probe in accordance with anembodiment.

FIG. 8 illustrates tracking and spatial registration of a probe inrespect to an investigated environment using an ultrasound rangingsystem mechanically registered to the probe in accordance with anembodiment.

FIG. 9 illustrates a tracking enabled gamma-ray probe used to detectsentinel lymph nodes in accordance with an embodiment.

FIG. 10A illustrates an ultrasound probe sharing a housing assembly withtracking and spatial registration camera and IMU in accordance with anembodiment.

FIG. 10B illustrates an ultrasound probe rigid housing assembly withtracking and spatial registration capability enabled by a machine visionsystem and an IMU mechanically registered to the probe in accordancewith an embodiment.

FIG. 11A illustrates a side view of an ultrasound probe assembly withtracking and spatial registration capability enabled by ranging systemsand an IMU mechanically registered to the probe in accordance with anembodiment.

FIG. 11B illustrates a rear view of an ultrasound probe assembly withtracking and spatial registration capability enabled by ranging systemsand an IMU mechanically registered to the probe in accordance with anembodiment.

FIG. 11C illustrates a rear view of an ultrasound probe assembly withdual-camera tracking and spatial registration capability enabled byranging systems and an IMU mechanically registered to the probe inaccordance with an embodiment.

FIG. 12A illustrates ultrasound readouts with probe tracking capabilityin accordance with an embodiment.

FIG. 12B illustrates alternative ultrasound readouts with probe trackingcapability in accordance with an embodiment.

FIG. 13 is a diagram of ultrasound methods that use tracking and spatialregistration capability in accordance with an embodiment.

FIG. 14 is a system diagram of a data flow for a virtual reality basedtelemedicine and guidance system in accordance with an embodiment.

FIG. 15 illustrates a graphical user interface (GUI) for an ultrasoundsystem with telemedicine, stereotactic and expert system guidancecapabilities in accordance with an embodiment.

FIG. 16 illustrates a spatially registered medical investigation, wherea camera or ranging system is supported by an operator's head-mountedtracking and visualization (HMTV) system in accordance with anembodiment.

FIG. 17A illustrates a front view of a probe, such as a dosimeter,radiation detector or chemical sensor, attached to a smart phone inaccordance with an embodiment.

FIG. 17B illustrates a rear view of the probe of FIG. 17A.

FIG. 17C illustrates a side view of the probe of FIG. 17A.

FIG. 18A illustrates a front view of a hand-held probe with anintegrated spatial registration system in accordance with an embodiment.

FIG. 18B illustrates a rear view of the hand-held probe of FIG. 18A.

FIG. 18C illustrates a side view of the hand-held probe of FIG. 18A.

FIG. 19 illustrates use of a computer vision camera combined with asingle beam lidar for hand-held probe spatial registration in accordancewith an embodiment.

DETAILED DESCRIPTION

Herein are described methods and systems using these methods aimed atproviding position and orientation (or spatial registration) for variousinstruments, such as hand-held probes, sensors, scanners, imagers orother instruments, with respect to investigated objects andenvironmental objects. An instrument can generically be referred to as a“probe.”

The purpose of spatial registration can be multiple-fold. One benefit isthe introduction of the capability to provide three dimensional (3D)models of the investigated objects. These 3D models can include multiplelayers of information, such as physical characteristics, as well asother characteristics provided by probe. Another benefit is thedetermination of the position and orientation of the probe inrelationship to the investigated environment. As a result of this, athree dimensional distribution of the quantity measured by the probe canbe determined. One dimensional (1D) or two dimensional (2D)distributions can also be determined, if found to be more relevant for agiven application.

The methods described herein can allow non-imaging probes, or imagingprobes with limited dimensionality, to provide superior threedimensional mapping of an investigated object. Two examples of probesthat may benefit from this aspect are: (1) ultrasound scanners formedical investigations, and (2) gamma-probes used for directed search ofradioactive hot spots. Other examples of sensing probes are an imaginggamma-ray camera, such as a Compton imager or collimator based imager,an ultrasound scanner or imager, a thermal infrared scanner or imager, aspectroscopic infrared scanner or imager, a ground penetrating radar,and a chemical sensor.

Besides the surgical arts, a field where aspects of the presentinvention can make an impact is in environmental surveys. Most commonly,the operator of a hand-held surveying sensor should specify a locationwhere a survey is performed in a manual fashion. Environmental surveyswould benefit from a method that would conveniently provide the positionand orientation of the system in relationship to the investigatedobjects or to the adjacent environmental objects and keep an automaticlog of the surveyed locations. This capability would also allow for anautomatic mapping of the investigated features. One particular exampleof an application that would benefit from such a capability is themeasurement of the radioactive dose or radiation field insidestructures.

Another field where aspects of the present invention can make an impactis in medical investigative and interventional procedures, as well astelemedicine. “Telemedicine” is broadly defined as the use oftelecommunications and information technologies to provide clinicalhealth care remotely. With the recent advances in broadbandcommunications and information technologies, the field of telemedicinehas received increased interest due to its potential to reducehealthcare costs and to provide quality healthcare services topopulations in isolated areas, or to patients experiencing decreasedmobility.

One particular component of telemedicine is remote clinical consultationand diagnosis. Particularly, ultrasound imaging is an attractive toolfor clinical evaluations at the point-of-care because of affordability,availability and convenience. These features make ultrasound imagingsystems suitable for use at multiple remote locations without the needfor an extensive support infrastructure. One obstacle preventing betterutilization and larger adoption of ultrasound imaging at thepoint-of-care is variable operator experience and training. Due to theultrasound-specific difficulty to find the proper “window” toinvestigate organs of interest, and because of limited imagingresolution, presence of artifacts and speckles, an ultrasound probe useror operator should have a very specialized training and have extensiveexperience to properly position the probe and to interpret the image,discriminating fine anatomical features from artifacts and speckle.Operator-dependent accuracy is one of the factors limiting theapplication of ultrasound in resource-limited settings. To overcomelimitations associated with varying levels of training and experience ofthe ultrasound operator at the point-of-care locations, existingteleconferencing systems allow a remote expert to assist theinvestigation process by providing verbal instructions to the localultrasound operator. This process can be cumbersome because of thedifficulty of verbally communicate instructions about how to bestposition the ultrasound probe in a 6-dimensional space (i.e., 3translations, 3 rotations), with a precision that should be less than2-3 millimeters translational resolution and less than 2 degreesrotational resolution. This positioning performance is sometimesrequired in order to capture clinically relevant image planes. Missingthe most relevant image plane by a few degrees is enough to missdiagnostically important anatomical features. In order to support theprocess of positioning the ultrasound probe, several previous approachesinvolved providing the local operator more information about the anatomyof the investigated areas in a virtual reality 3-D model. The purpose ofthis approach was to make the local operator more situationally aware ofthe anatomical structures being investigated. These solutions involvecomplex augmented reality systems, and they still don't provide a meansfor a remote trained user to efficiently guide the local operator thebest course of action.

In embodiment, different methods and systems that are easier and cheaperto implement than those in the prior art are disclosed. In addition,methods and systems are proposed that allow operators to receiveinstructions from automated computer guidance systems, previously savedprotocols, stereotactic markers, or a combination of these—circumventingthe need for assistance from a trained operator.

“Stereotactic ultrasound” is taught herein, as opposed to stereotacticimaging. Stereotactic imaging, especially using CT and MRI, is beingused to guide biopsies and other surgical procedures. In its most broadinterpretation, stereotactic imaging refers to the capability of animaging system to identify, label and register anatomical features ofinterest in 3-D so that follow up medical interventions andinvestigations can use those same 3-D coordinates to precisely guidemedical instruments, or for re-evaluations. A stereotactic ultrasoundinstrument in accordance with an embodiment can be able to labelfeatures of interest in 3-D and register them in respect to anatomicallandmarks so that follow-up investigations can easily use thosecoordinates to re-evaluate various medical conditions.

Another aspect of some embodiments is to provide a user, such as asurgeon or a physician, the capability to track objects in the field ofview in respect to each other by using a camera or ranging system placedon another object or on a head-mounted tracking and visualizationsystem. There is no need for using separate tracking cameras or lightemitting devices.

Advantages

Among other aspects, some embodiments make use of the latest advances inranging systems, such as time-of-flight cameras, lidar systems,structured light systems, electromagnetic sender-receiver assemblies,and sonar systems, which allow for a construction of a physical model ofthe environment and for positioning and tracking of instruments and/orsensors probes in respect to said physical model.

Among other aspects, some embodiments make use of the latest advances incomputer vision algorithms which, by using simple and inexpensive visualcameras in conjunction with fiducial markers placed on instruments, onsensor probes, on an investigated object or in the environment, providepositioning and tracking of instruments and/or sensors with respect tothe investigated subject or environment, as well as creates a physicalmodel of the investigated subject or environment.

Thus, several advantages of one or more aspects are to providepositioning and orientation of mobile sensors and instruments in theenvironment in a convenient and inexpensive way. Other advantages of oneor more aspects are to provide spatial tracking and logging of thesensors and instruments. Other advantages of one or more aspects are toprovide the spatial information necessary to reconstruct theinvestigated field in one dimension (1-D), 2 dimensions (2-D) or 3dimensions (3-D). Other advantages of one or more aspects are to providea modality for a remote user to communicate its choice to a localoperator, human or robotic, in what regards the position and orientationof an instrument or sensor in respect to the environment, investigatedsubjects or other instruments. Other advantages of one or more aspectsare to provide capability for stereotactic investigations usingultrasound.

“Stereotactic ultrasound” is a capability to label features of interestidentified by an ultrasound scanner and register them in respect toanatomical landmarks so that follow-up investigations can use thosecoordinates to re-evaluate or treat various medical conditions, or asotherwise known in the art. Other advantages of one or more aspects areto provide computer guidance to operators of sensors and instruments.Other advantages of one or more aspects are to provide an intuitivevisualization and graphical interface to local and remote operators whenhandling sensors and instruments.

Another advantage of some aspects is to allow a user, such as aphysician or surgeon, to interact with a computer by moving objects,parts of his or her body without the need to physically touch a humaninterface while having the possibility at the same time to track theposition and orientation of instruments and sensor probes in respect toeach other and in respect to the user, and to manipulate medicalinstruments or sensor probes.

These and other advantages of one or more aspects will become apparentfrom a consideration of the ensuing description and accompanyingdrawings.

Figures and Descriptions

FIG. 1 shows a first modality by which spatial registration can beprovided to a probe. A ranging device camera RS 102 is mechanicallyregistered to the probe P 101 through a mechanical mount 103. The wholeassembly, which is made out of components mechanically registered to theprobe 101, can be called a “probe assembly.”

Examples of ranging device cameras that can be used are: atime-of-flight camera, a structured light camera, or a lidar scanner.

A computing unit 104, which may or may not be mechanically registered tothe probe-ranging device assembly, receives data or electrical signalsfrom the probe and transmits data or electrical signals to the probethrough connection 105, in the case when such data or signals arenecessary, and from and to the ranging camera 102 through connection106. Connections 105 and 106 can be wireless or made out of physicalcables. The computer 104 receives, processes, and synchronizes datacoming from probe and ranging camera and performs further processing.

The investigated subject or environment 107 and 108 are on the left sideof the figure. The ranging camera 102 emits a signal which back-scattersoff the objects carrying information with regard to distance to thoseobjects. In this figure, the signal emitter is represented by 109, aninstantiation of the emitted signal is represented by dashed line 110,the reflection from the object in the direction of the signal receiveris represented by line 111, and the signal receiving sensor of theranging camera system is represented by 112.

In a “time-of-flight (TOF) ranging camera”, the emitted signal is a timemodulated or pulsed light that illuminates the parts or the wholefield-of-view (FOV) of the receiver 112, preferably emitted by a laseror a Light Emitting Diode (LED), and the signal receiver 112 is a timeof flight camera. In the case of a structured light ranging camera, theemitted signal can be infrared (IR), visual or ultraviolet (UV)structured light or modulated light system, and the signal receiver is aIR, visual or UV light camera. In this case, the spatial distance (orlever arm) between the source 109 and receiver 112 can be optimized toprovide best range resolution for the intended range of distances.Processing of data from these systems to get 3D models of objects can beperformed with stereoscopic algorithms. In the case of a lidar scanner,the emitted signal is a pulsed laser beam, and the receiver is a lightsensor able to measure time-of-flight information by direct energydetection or phase sensitive measurements. In the case of a 3D flashlidar, the emitted signal is a pulsed laser beam illuminating the wholefield of view (FOV), and the receiver is a specialized light sensingarray able to measure time-of-flight information. The computing unit 104will analyze the range data to determine the relative translation androtation of a coordinate system 113 associated with the probe 101 inrespect to an arbitrary coordinate system 114 associated with theadjacent environment or investigated objects.

The lidar ranging camera, or other time-of-flight camera, can havecommon optics for the emitter and receiver.

For increased ranging performance, the light source 109 can be made outof multiple physically separated units, and the signal receiver 112 canbe made out of multiple receivers physically separated, but mechanicallyregistered to each other. An example when such an implementation canbring benefit is when using a structured light ranging camera. Placingthe source of the patterned light between two or more light cameras willinsure that the pattern projected by the source will be seen by at leastone camera. Moreover, superior ranging precision can be obtained byusing the stereoscopic-like information provided by any combination ofmultiple such cameras.

For increased tracking performance, the ranging camera based trackingsystem can be combined with other tracking systems, such as an inertialmeasurement unit (IMU), computer vision system, or ultrasound orelectromagnetic ranging systems.

Another example of merging various ranging and tracking systems is whena lidar system is used jointly with an IMU system for spatialregistration. The operator will scan the environment with the lidar, andthe IMU will provide dead reckoning information. Combining the two data,spatial registration of the probe in respect to the adjacent environmentcan be obtained.

FIG. 2 shows an example of how the range data can be used to provide therelative position and orientation of the probe in respect to theinvestigated objects and adjacent environment, and how that can be usedto build more complete models of the features mapped by the probe in thecase when the probe is a sensor.

The data coming from the ranging and tracking camera 102 (see FIG. 1 )are fed into a data acquisition system 201. In order to obtain trackinginformation from range data, a previously stored 3D space model 202 isused as a reference. This model represents the outline of the objects inthe environment and could have been created during a previousmeasurement session, or from computer generated models such as computeraided design (CAD) models, or during the same investigative session,from previously recorded range scans. If no previous 3D models exist, ablank state can be assumed. For each moment of time, the range andtracking data is merged with the pre-existing 3D space model 202 by apose estimator module 203 that matches the current range data with thepre-existing 3D model. Because the current range data may only partiallyoverlap with the pre-existing 3D model, conditions for what fraction ofthe scanned surfaces should overlap will depend on the application. Fromthis process, the pose of the ranging sensor in respect to the 3D modelof the environment is determined. In support of the process, othertracking sensors, such as IMUs, can be used to constrain the search forthe best fit, and the best pose.

The result of this process will be an extension of the pre-existing 3-Dmodel with the current range data. This is done as part of step 204. Theresulting model can be used as a pre-existing 3-D model 202 for the nextframes. At the same time, the data coming from the sensor probe 101 (seeFIG. 1 ) is fed into the probe data acquisition and analysis module 205.After the probe data is synchronized with the tracking (or poseestimate) data, an Object Structure Reconstruction module 206 is used tobuild a volumetric distribution of the features mapped by the probe.

At step 206, at each moment in time, the probe data is associated withthe spatial position and orientation of the probe provided by themachine vision system to create spatially registered data. This allowsthe system to track the amplitude of the probe data as function of theposition and orientation of the probe in space, allowing for areconstruction of the spatial distribution of the investigated field oreven of the source term.

The “source term” is the source of the amplitude values measured by theprobe. For example, for a gamma-ray probe, the source term is thegamma-ray source, which most commonly is a radioactive tracer; for anultrasound sensor, the source term is the sound scattering andreflecting properties of the investigated material. For a chemicalsensor, the source term is the source of a chemical element or moleculeof interest.

The “investigated field” mentioned above can be the radioactive dose, ifa radiation detector or a radiation dosimeter is used. It can bechemical concentrations, if a chemical sensor is used, etc.

In order to perform the reconstruction of the source term distribution,various algorithms that resolve inverse problems can be used. In thisway, a higher dimensionality model (2-D or 3-D) of the features mappedby the probe is obtained. The information about the probe position andorientation can be also used along with the output of the 3-D spacemodeler 204, the 3-D contour of the investigated objects and/orenvironment, to constrain the solution of the distribution of fieldmapped by the probe, for better visualization and for spatialregistration of the investigated field in respect to the environment.

A visualization module 207 may be used to visualize the various modelsfor user inspection and analysis. The visualization module may alsoinclude a user interface capability which allows the user to navigatethe models, change visualization options, change system settings, andobtain supplementary information about the various components of thescene. Examples of visualization modules are: a computer screen, a touchscreen, augmented reality devices or goggles, projectors, head mounteddisplays. All or parts of the ensuing models and data can then be savedfor follow up inspections or further processing in module 208.

FIG. 3 shows another approach to provide the position and orientation ofthe probe 301 in respect to the investigated objects or adjacentenvironment. In this case, probe tracking information and the outline ofthe 3-D model of objects are obtained by using mostly passive lightsensing components. A light sensing device 302, such as a highdefinition video camera, is mechanically registered to the probe 301through a mechanical connection 303. The whole assembly made out ofcomponents mechanically registered to the probe 301 will be called“probe assembly.”

The opening for light collection is represented by 304. Similar to theembodiment of FIG. 1 , a computing unit 305, which may or may not bemechanically registered to the probe-ranging camera assembly, receivesdata from the probe and transmits data to the probe through connection306, in the case when such data is available, and from and to the lightsensing system 302 through connection 307. Connections 306 and 307 canbe wireless, or can be made out of physical cables.

The computer 305, receives and synchronizes the data coming from theprobe and ranging camera and performs further processing. Theinvestigated subject or environment 308 and 309 are at the left side ofthe figure. A fiducial object 310 with well-defined measurements may bemechanically registered to the investigated object to provide areference system associated to the investigated object, to provide scaleto the scene, and to provide features or landmarks that are easy toidentify and to track.

Various examples of fiducial objects are presented in FIGS. 4 and 5 .Ambient light can be used to illuminate the fiducial marker 310, or thefiducial marker could comprise active light sources, such as IR orvisible LEDs. A light source connected to the tracking system can beused to illuminate the scene.

The light scattered or emitted by the fiducial marker is represented bythe dashed-arrow 311 (FIG. 3 ). A perspective n-point algorithm can beused on the computer 305 to process the apparent shape of the fiducialas seen by the light sensor 302 to determine the relative translationand rotation of a coordinate system 312 associated with the probe 301 inrespect to a coordinate system 313 associated with the fiducial marker.Since the fiducial marker is mechanically registered to the investigatedobject, the coordinate system 313 can be interpreted as being attachedto the investigated objects.

Additionally, the probe assembly may comprise a light source 314 to moreeasily highlight the fiducial object 310 or marker, as well as theinvestigated objects. The light output opening 315 is on light source314. An instantiation of the emitted light represented by dashed arrow316 is shown falling on the object 309, and a scattered light photongoing towards the light sensor 302 is represented by the dashed line317. Similar rays of light will fall on all objects in the field of viewof the system, including on the whole or parts of the fiducial object310.

Structure from motion algorithms can be implemented on the computer 305to construct the 3-D model of the outline of investigated objects andadjacent environment, when the probe system is moved in space. Toincrease probe tracking performance, an IMU 318 can be mechanicallyregistered to the probe assembly.

For spatial registration redundancy, the fiducial objects 310 can alsocomprise other spatial registration elements, such as electromagneticreceivers as 709 in FIG. 7 or ultrasound receivers as 807 in FIG. 8 .These receivers can be used in conjunction with electromagnetic emitters702 in FIG. 7 and ultrasound emitters 802 in FIG. 8 , respectively.

Additionally, the light sensing system can comprise an assembly of twoor more light sensing devices, such as a stereoscopic system made of atleast two video cameras that have an overlapping field of view. Oneadvantage of using an assembly of light sensing devices is an increasedfield of view. Another advantage of a stereoscopic system, inparticular, is that for the 3D modeler analysis step described below (instep 604 of FIG. 6 ), to be implemented on computer 305, the scale ofthe investigated scene will be apparent from matching the frames takensimultaneously from the multiple cameras, whose relative positions andorientations can be known with high precision. Also, in this arrangementno movement of the system is necessary to construct the 3D model of theinvestigated object.

In this figure only two light sensing devices are shown. The secondlight sensing device 319 is shown mechanically registered to the probeassembly with a precise relative position and orientation from lightsensing device 302. Stereoscopic algorithms can analyze the sensing datafrom the two light sensing devices to calculate the position andorientation of the probe in respect to the investigated objects and toincrease precision in the determination of the 3-D model of the outlineof investigated objects and adjacent environment. The opening of thelight sensing device 319 for light collection is represented by 320.More than two units can be used in order to get more completeinformation from the same FOV or to increase the overall instrument FOV.

Additionally, a similar computer vision camera system can be mounted onother sensors and instruments that can be used simultaneously with probe301. The spatial tracking data from all these elements can be combinedto create a common spatial model comprising instruments and investigatedfields. An example of an application using this setup is theintraoperative use of an ultrasound scanner along other surgicalinstruments. The ultrasound scanner and the surgical instruments caneach of them be fitted with computer vision camera systems, or some ofthe components can comprise elements which act as fiducial elements.

Examples of light sensing devices are charge-coupled devices (CCD) orcomplementary metal-oxide semiconductor (CMOS) sensors. Embodimentsusing this method can include cameras that are sensitive to visibleand/or infrared radiation. As such, the light source may emit in visibleor IR. The camera(s) can also be a light-field camera, also called aplenoptic camera, a hyperspectral camera, or a compressive sensingcamera.

One purpose of the fiducial object 310 is to help the computer visionsystem better determine the scale of the whole scene, to unambiguouslyposition the probe in the scene, and to provide a landmark for 3-Dmodeling of the object outline. A fiducial object can be referred to asa “reference object.” Alternatively to a fiducial object, a fiducialmarker, such as a label with clearly distinguishable features can beplaced on various objects in the environment.

The data stream (or video stream) coming from the light sensing device(or camera) is analyzed to identify the fiducial object in the field ofview. By analyzing the apparent form of the fiducial object, theposition and orientation of the probe in respect to the fiducial objectis obtained, and from that, the position and orientation of the probe inrespect to the investigated object.

FIGS. 4A and 4B illustrates fiducial objects in accordance withembodiments. In FIG. 4A, the fiducial object 401 is in a bar shape in astraight angled elbow that is painted in a pattern of contrastingcolors. Alternatively, painted reflective material can be used toimprove visibility. In FIG. 4B, the fiducial object includes a frame 403that supports four spherical objects 402. These spherical objects can beeither devices actively emitting light, such as light emitting diodes(LEDs), or can be objects made from a material that is efficient atdiffusely reflecting the IR or visual radiation.

A particular fiducial object that may be suitable to provide fiducialmarking to a large surface area are piece-wise rigid bands. Each rigidpiece can have a pattern similar to the QR or AR codes, but optimizedfor pose estimate determination. An example of such a fiduciary is shownin FIG. 5 . The substrate tape 500 of the fiducial object can be laid onan investigated object (such a as patient in medical investigations) inan area close enough to the area to be investigated. This substrate canbe made from a flexible material such as rubber, elastomers, such assilicone, polyurethane and latex, or other material flexible enough tofollow the layout of the object.

The backing that will be towards the patient can be made of the samematerial or a different material that is adhesive enough to not allowthe fiducial to slide easily across the skin or cloths of the patient.The figure shows a fiducial in the form of the letter I. Otherarrangements are possible, such as a in a form of a L, T, V, U, or otherpattern, the choice of which can depend on the particular area to beinvestigated.

One or more rigid pieces can be mounted on this form. Several suchfiducials can be used concurrently. These rigid pieces are shown in thefigure by 501, 502, 503 and 504.

On each of these pieces, a pattern can show distinguishable featuresthat allow the machine vision system to get a physical scale of theenvironment, get a pose estimate, and uniquely identify the type offiducial, and the place of the piece within the whole fiducial. Some ofthese features are indicated for the 502 piece. Corners 505, 506, 507,and 508 made by the black squares in the four corners of the 502 piecewith the central large square will provide most reliable information tothe machine vision analysis to determine scale of the environment andcamera pose. The middle pattern 509 will comprise a distinct binary codethat will uniquely identify the corners 505, 506, 507, and 508, as wellas the fiducial type, index, and the relative position of the patternwithin the whole fiducial.

A more detailed example of an implementation of the data analysis chainwhen using passive light sensing devices is shown in FIG. 6 . In theembodiment, there are two main streams of data, one coming from theprobe, when applicable, the other coming from the light sensing devices(or computer vision cameras). The data coming from the computer visioncameras is analyzed by a computer vision analysis chain.

In most implementations, the image frames have to be rectified tocorrect for the distortion of the optics and to account for the responseof the camera to points at various positions in space. Therefore, animage rectification 601 analysis step may be used to correct theposition of the pixels in the frame using a pre-measured calibrationmatrix. The calibration matrix is obtained by taking various pictures ofknown 3D objects or 2D planes positioned at different angles andpositions in the field of view. The calibration and rectificationmethods are commonly known in the field.

The second computer vision analysis step 602 identifies the fiducialobject or fiducial marker in the field of view, and uses its apparentshape to determine the position and orientation of the computer visioncamera in respect to that fiducial object in the following poseestimator step 603. Since the camera is mechanically registered to theprobe, a position and orientation of the probe is determined by simpletransformations. In the case in which a fiducial object is not used,various features of the investigated objects or in the environment canbe used as reference points.

Whereas when fiducial markers are used, the movement of the computervision system in respect to the investigated objects may not benecessary; when fiducials are not used, the algorithms under this step603 may require the observation of the investigated object by thecomputer vision camera or cameras from various angles.

A 3-D modeler (or dense machine vision) step 604 may also be used todetermine object parameters, such as 3-D models of the contours of theobjects being investigated or from the adjacent environment. Buildingthe contour 3-D model reliably using dense machine vision 604 algorithmsmay also require the observation of the investigated object by thecomputer vision camera or cameras from various angles. Various featuresin the field of view are tracked in time across frames takensuccessively as the camera is moved, and a full 3 dimensional positionof the object features is calculated, as in step 604. This process usescomputer vision algorithms that create 3-D structure from video.

Structure from motion algorithms can be used to build the 3-D contour ofthe investigated object, environment or patient. This contour 3-D modelcan be integrated into the common virtual 3-D model of the setup. Theregistration of the probe within the virtual 3-D model can be obtainedby analyzing the apparent shape of the fiduciary object, as seen fromthe computer vision camera on a computer device.

The problem of estimating camera pose from observing pre-definedfiduciary points is known in the computer vision field as theperspective-n-point problem (PnP).

A linear solution that requires four points for a unique solution waspublished in Ansar A, Daniilidis K., “Linear pose estimation from pointsor lines,” Pattern Analysis and Machine Intelligence, IEEE Transactionson 2003; 25:578-89, which is hereby incorporated by reference.

More recently, Lepetit V, Moreno-Noguer F, Fua P. “An Accurate O (n)Solution to the PnP Problem,” International Journal of Computer Vision,2009; 81:155-66, which is herein incorporated by reference, presented an0(n) solution for n>=4.

For a strictly 3 point solution, Xiao-Shan G, Xiao-Rong H, Jianliang T,Hang-Fei C., “Complete solution classification for theperspective-three-point problem,” Pattern Analysis and MachineIntelligence, IEEE Transactions on. 2003; 25:930-43, which is herebyincorporated by reference, describes another approach suitable for thisapplications.

Present embodiments using computer vision systems and inertialmeasurement units for probe tracking eliminate shortcomings of otherapproaches for tracking, such as the need for external, bulky opticaltrackers or magnetic emitters, the need to maintain a long line ofsight, or the need to maintain a “clean” magnetic environment. One ofthe problems associated with determining structure from video is thedetermination of the scale of the object. To resolve this problem, thefiducial object or marker, which is of known shape and dimensions, canbe used to determine the right scale, providing exact object dimensions.Examples of fiducial objects are described above and in FIGS. 4A-5 . Thefiducial object can also be used to define the reference system for thewhole scene. If fiducial objects or markers are not available, theproper scale can be determined by using either a stereoscopic computervision system, a lidar system, a ranging camera, an Inertial NavigationUnit (INU), or a combination of these, each of which registered to theprobe or integrated into the probe.

The data coming from the probe, when available, is read-out and adjusted(see step 605) to be used in the 3D Object Structure Reconstructionanalysis step 606. The information about the probe position can beassociated with the probe data coming from the probe data acquisitionand analysis step 405 to create spatially registered data.

This spatially registered data can be used to build a 2-D or 3-Ddistribution of the features mapped by the probe. This is done under the3D object structure reconstruction process 606. From here on, steps 606,607 and 608 are similar in function with step 206, 207 and 208 of FIG. 2, respectively, and their description is appropriate here.

In an alternative mode of operation, no fiducial objects or markers areused. In such a case, or when the fiducial objects or markers are not inthe field of view, step 602 can be skipped, and the data from step 601will go directly to step 603. This operation mode may be more common inbroad area surveillance and mapping applications, where the use offiducial objects or markers may not always be practical. In this case,an estimate of the 3D position and orientation of the camera is obtainedby tracking features and highlights associated with various objects inthe field of view in subsequent image frames. By triangulation, thedistance to these highlights can be calculated, and from that, thespatial registration of the sensor in respect to these highlights isdetermined. At the same time, the 3D model of the whole scene can bebuilt. However, if there is no reference (or fiducials) in the scene toindicate the absolute scale of the scene, the determined dimensions haverelative values.

To get an estimate of the absolute values in this case, otherpositioning systems can be combined with the computer vision system,such as an inertial measurement unit (IMU), a laser based range finder(LIDAR), or any combination of these. Even though tracking of positionsand orientations using IMU dead reckoning may lead to drifts over itsuse, by combining the information from dead reckoning with the computervision-based spatial registration, improved positioning can be achieved.

A lidar system using a laser beam (or several beams) can be used to getthe absolute distance to objects in the environment for selected points.By identifying the points where the laser beam hits an object in thecamera frames, and by using the absolute distance values provided by thelidar system, the absolute scale of the scene can be deduced. The figureincludes the implementation in which the tracking and spatialregistration system uses an external tracking or ranging camera, such asan IMU, a LIDAR, or other system.

If other tracking systems are used synchronously, such as IMUs, orranging cameras, their corresponding data stream is read out in step609, and merged with the camera data in step 603 to improve poseestimate performance by using multi-sensor filters, such as Kalmanfilters. For example, in step 609 data from an IMU can be used fordead-reckoning or the range data from a LIDAR is used for laser ranging.

In yet another implementation, a fiduciary marker or object can bemechanically registered to the probe, and a computer vision trackingsystem or a ranging camera external to the probe can be used to observethe spatial field where the probe will be used. The data from theexternal tracking and ranging camera can be read-out by a computer unit.For increased performance, another tracking system, such as an IMU,registered to the probe can be used. The data from this tracking systemcan be read-out by the same computing unit that reads the externaltracking and ranging camera.

FIG. 7 shows a tracking system that uses electromagnetic waves forranging. An example of electromagnetic waves is magnetic fields.Electromagnetic pulses, including magnetic fields, can be used but inwhich the active electromagnetic elements are placed inside theinstruments and sensor probes, and are used as active elements emittingelectromagnetic fields. The electromagnetic sensors inside referenceobjects are used as passive elements. An advantage to this mode ofoperation is that the amplification electronics required to amplify thesignal detected by the passive electromagnetic sensors can be placedvery close to the sensors, eliminating the need for long wires betweenthe sensors and amplifiers, reducing noise pick-up.

Examples of electromagnetic sensors are magnetic sensors, such as coils.Since the magnetic sensors are directional, a set of three magneticsensors oriented orthogonal to each other will be enough to provide theposition and orientation of the probe in 3D in respect to the referenceobject, if a set of 3 orthogonal active magnetic elements are placed inthe probe, and emit magnetic pulses.

An electromagnetic transmitter 702 is mechanically registered to theprobe 701 through the mechanical mount 703. Similarly to FIGS. 1 and 3 ,a computing unit 704, which may or may not be mounted to theprobe-ranging device assembly, may send and receive data from the probethrough connection 705, in the case when such data is available, andfrom and to the electromagnetic transmitter 702 through connection 706.Connections 705 and 706 can be wireless, or can be made out of physicalcables.

The computer 704, receives and synchronizes the signals and data sent toand coming from the probe 701 and electromagnetic transmitter 702, andperforms further processing. The investigated subject or environment isabstractly represented by the rectangular boxes 707 and 708. Anelectromagnetic receiver 709 is set on or mounted to an investigatedobject or instrument in relation to which tracking of the probe 701needs to be done.

By analyzing the intensity and/or the phase of the electromagneticsignal transmitted by the transmitter 702, relative position andorientation of the coordinate system 710 associated with the transmitter702 in respect to a coordinate system 711 associated with the receiver709 can be obtained, hence the relative position of the probe assembly.

The signal received by 709 is transformed into data that can betransmitted to a computer, such as 704 through cables or wirelessly. A“type of signal” that can be used for such a positioning method is amagnetic signal. In the present embodiment the transmitter ismechanically registered to the probe.

Alternatively or additionally, unit 709 can be used as anelectromagnetic emitter and unit 702 can be used as an electromagnetictransmitter. In this case, the emitter 709 will emit electromagneticfields that will be detected by the electromagnetic sensors 702mechanically registered to the probes.

In another implementation, multiple signal receiving elements can beused for better estimation of the relative position and orientation, orfor getting the tracking information for multiple components, objects,instruments of sensors.

FIG. 8 shows another tracking system that uses assemblies of ultrasoundtransmitters and receivers. The setup has a few elements similar to theembodiments of FIG. 1, 3 or 7 . In this embodiment, an ultrasoundtransmitter 802 is mechanically registered to the probe 801 through amechanical connection 803. Lines 804 and 805 are data connections fromthe probe 801 and transmitter 802, respectively, to a computer 806. Theultrasound receiving system 807 is an assembly of multiple individualreceivers mechanically registered to each other placed on an object 808.

In this figure, three such receivers are shown. Objects from theenvironment 808 and 809 are on the left side of the figure. Thecoordinate system associated with the probe is 810; the coordinatesystem associated with the receiver is 811. The transmitter emitsultrasound pulses 812 of frequencies preferably above human hearingrange, but low enough to insure transmission through air. The receivedsignals can be transformed into data and transferred to the computer 806wirelessly or using cables. By measuring the time of flight andintensity of the ultrasound waves for each individual receiver, theposition and orientation of coordinate system 810 can be found inrespect to coordinate system 811. The calculation can be done on thecomputer 806 or on a processor integrated with the receiving system 807.

Thus, since the proposed methods of merging spatial registration systemswith various sensor and instrument probes provide tracking and loggingof the said probes with high precision in an efficient, inexpensive andcompact package, another one of several advantages are to provide thespatial information necessary to reconstruct the investigated field inone dimension (1D), 2 dimensions (2D) or 3 dimensions (3D).

An application where some aspects of the present invention cansignificantly make an impact is in the detection of the sentinel lymphnodes using gamma-ray probes. Gamma-ray probes are currently used fornavigated sentinel lymph node dissection in intra-operativeapplications. It is of interest to locate and extirpate the lymph nodes(also known as sentinel lymph nodes) that receive the lymph drainingfrom the general area of the cancerous tumor because these are the firstplaces where cancer cells can propagate.

Typically in a lymph node detection application, a solution containing aradioactive tracer, such as Tc-99m, is injected inside the tissue nearthe tumor so that it will drain into the sentinel lymph nodes.Subsequently, a collimated gamma-ray detector is used by a surgeon todetermine the position of the sentinel lymph nodes by monitoring thecount rates detected by said collimated radiation detector as thesurgeon moves the gamma-probe around the relevant body areas. A trackingand spatial registration system mechanically registered to a gamma-rayprobe can provide the spatial tracking of the gamma-ray probe as theprobe is moved around the investigated human body. This will allow thesurgeon to get a full three-dimensional distribution of the injectedTc-99m inside the patient and to have that distribution spatiallyregistered to the body of the patient and/or the gamma probe itselfand/or other instruments.

FIG. 9 shows an example of an embodiment that accurately and reliablydetermines the position of the lymph nodes. A patient is represented bythe torso shape 900. A gamma-ray probe is made out of a probe head 901,handle 902 and tracking system 903 connected to the probe handle by anarm 904. The gamma probe assembly can be made out of an integratedstructure, or the tracking system can be mounted on the gamma-probehandle using a mounting mechanism 905 such as a bracketed structure. Themechanical structure will insure high mechanical registration betweenthe gamma-ray probe head 901 and the tracking system 903.

The gamma-ray probe head 901 comprises a gamma-ray detector, such as asemiconductor detector or scintillator, surrounded by a collimator thatallows gamma-rays from a limited field of view to enter the detector.The field of view of the gamma-ray detector is represented by the cone906. A distribution of gamma-ray radioactive tracer, such as Tc-99m isrepresented by the patch 907, which is inside the body of the patient900.

Streams of digital data or analog signals coming from the gamma-raydetector are read out by a read-out and processing unit through a cable908. This cable can contain wires that also read out the tracking system903. Alternatively, the tracking system can be read-out through aseparate cable 909. The data coming from the tracking unit and from thegamma-ray detector will be synchronized inside a read-out processingunit. The tracking system can be any of the tracking modalitiespresented above.

In the present embodiment, the tracking system is a machine visionsystem comprising 3 main elements: (1) a light sensing device 903, suchas a video camera, that is appended with high mechanical registrationprecision to the handle of the gamma probe 902; (2) an active or passivefiducial object, or objects 910, 911, 912, 913 that can be mounted orlaid on the patient 900 and that contains active or passive featureseasily identifiable by the camera 903 (whereas active features can belight emitting elements, passive features can be painted forms); and (3)a data acquisition and processing module, such as a computer that readsthe video stream and integrates it with the information obtained fromthe gamma probe.

The field of view for the computer vision camera 903 is representedgenerically by the opening angle 914. A spatial registration systemsimilar to 903 can be mechanically registered to other surgicalinstruments to allow tracking their position in space in respect to thesame fiducial objects 910, 911, 912, and 913. This spatial registrationsystem will be read out by the same computer that reads the data andanalyses the tracking information provided by 903. This will allowreal-time positioning in a common virtual model of all elements ofinterest, such as all relevant instruments, the gamma-ray probe, theinvestigated patient, the map of the radioactive hot spots indicatingsentinel lymph nodes and potential cancerous tissue, etc.

Alternatively, a ranging system as described in FIGS. 1, 7 and 8 , canbe mechanically registered to the gamma-ray probe and other instrumentsto provide gamma-probe tracking for the lymph node detectionapplication.

There are several advantages associated to the present lymph nodedetection approach: better sensitivity, better location, lower radiationdose, faster process, and a shorter surgical procedure.

Another important application of the present methods is in medicalsonography. Tracking and spatial registration systems, as presentedabove, mechanically registered to an ultrasound scanner can providespatial tracking of the ultrasound probe as the probe head is movedaround an investigated object, such as a human body. An improvedultrasound investigation will benefit especially from using rangingsystems or passive light sensing systems used with fiducial objectsplaced on the investigated body, or mounted to a fixed structureadjacent to it. This spatial tracking will allow an algorithm running ona computer to merge the 2-dimensional images created by the ultra-soundscanner into a 3-dimensional model. This will effectively transforminexpensive 2D ultra-sound scanners into 3D scanners. This applicationcan be referred to as “freehand 3D ultrasound imaging.” Spatial trackingof the ultrasound scanner using a tracking system mechanicallyregistered to the ultrasound probe has other multiple advantagescompared to other tracking systems known in the field:

It uses inexpensive ranging, IMUs or camera systems; it is compact,easily transportable, and the setup of the assembly is very fast.

The delivered positioning and orientation precision is not largelyaffected by the presence of metallic objects of other external magneticfields as the magnetic trackers.

A line of sight needs to be maintained from the computer vision camerato the fiducial object for best performance, or from the ranging systemsto the investigated and adjacent objects, but this line of sight is veryshort as compared to CMM-based systems, and therefore, much easier tomaintain.

When the line of sight to the fiducial or to the patient is broken,position and orientation can still be determined from using poseestimate algorithms by observing other adjacent objects. Additionally,IMUs, ultrasound speckle decorrelation tracking, ultrasound rangingsystems and electromagnetic ranging systems can be used for redundancy.A “merging” algorithm can be used to integrate the information providedby all these tracking elements.

These and other benefits give spatial registration systems mechanicallyregistered to the ultrasound probe a clear advantage for freehandultrasound imaging. Moreover, this implementation will also allowultrasound scanners with 3D transducers to have larger effective fieldof views by overlapping multiple 3D scans taken at various angles andpositions. Furthermore, it will also allow better use of the 2D imagesby spatially registering them.

Another advantage of this approach is that by keeping track of thesuperposition of the scans and observing the same structures fromvarious angles and positions, it is possible to identify and correctultrasound specific artifacts, such as reverberations, refractions,ghost images, “comets”, etc.

Yet, another advantage of this approach is that in the intraoperativeuse of ultrasound to navigate medical instruments, the user, or theoperator will have much more confidence in the ultrasound models, sincethe organs and structures will be spatially much better defined, withmuch reduced artifacts. The surgeon will be able to follow in real time,in a common virtual model, all elements of interest, such as the medicalinstruments, the ultrasound scanner, the investigated body, the 3Dultrasound model of the organs, and potentially, other pre-operativemodels. Moreover, image segmentation algorithms can be used in theprocess of merging the 2D ultra-sound images into the 3D ultra-soundmodel and to delimitate various features in the 3D model, such asorgans, tissues, etc. Computer expert systems can also be employed toidentify anomalies and other specific features that are clinicallyrelevant.

Among other aspects, the present invention also describes an inexpensiveand efficient way to create a virtual reality model of an adjacentenvironment that can be used for better operator guidance and feed-backduring telemedicine applications and for superior overall clinicalresults by providing a common reference space for one or more medicalinstruments used during the clinical procedure and for data that iscollected in time from one or more sensors. The virtual reality modelmay comprise multiple elements, among which are:

a contour 3-D model of the patient;

an interior 3-D model of the patient, that can be made of organ 3-Dmodels, previously taken imaging data, current sensory data;

medical instruments and sensors, as they move in space and time;

data from sensors;

other elements that may guide the operator or may help the operatorperform superior, reliable clinical procedure, such as virtual objects,rendered volumes, pointers, values, etc.

similar elements as in the previous points, but sent over a network froma remote user or computer system.

At the core of the embodiment is the use of a ranging camera and/or apassive camera, which is attached to either one of the medicalinstruments or sensors, or it is positioned to observe the environmentcomprising the patient, medical instruments, and potentially, the localclinician. This approach is exemplified by using an ultrasound imagingapplication.

FIGS. 10A-10B show examples of two ultrasound probe housings thatcomprises passive machine vision cameras and IMUs mechanicallyregistered to the probe for probe tracking.

FIG. 10A shows an ultrasound probe housing assembly with a detachablecamera housing shell. An ultrasound imaging probe housing shell 1001 isin contact with the investigated patient 1002 through the ultrasoundprobe head 1003 which comprises an ultrasound transducer. The ultrasoundtransducer can comprise a mechanically scanned transducer, a phasedarray of transducers, or a combination. Mechanically registered to theprobe is a camera housing shell 1004 comprising a camera whose lenses1005 are oriented in the general direction of the patient. In thisembodiment, the communication with the ultrasound probe inside housing1001 is done through a cable 1006, which can be an universal serial bus(USB) cable or other type of cable that goes to a read-out device. Thisread-out device can be a computing unit, such as a laptop, computer,tablet, or a smart phone, or a routing device when the housing 1001 ofthe probe comprises electronics able to create beam-forming signals tobe sent to the transducers and to read-out and condition the signalsreceived from the transducers. Otherwise, the read-out device willcomprise beam forming and signal conditioning electronics, as well as acomputing unit.

The data transport between the computing device and the camera can bedone wirelessly or through a cable 1007, which can be an USB, FIREWIRE®,or other cable that ultimately sends the computer vision data to acomputing unit that also receives data from the ultrasound probe.

An Inertial Measuring Unit (IMU) 1008 may be integrated into the probehousing shell 1001, into the camera housing shell 1004, or in any otherway mechanically registered to the ultrasound probe. Here the IMU isshown inside the body of the ultrasound probe housing shell. The IMUcould be used by itself, or in conjunction with the camera, or inconjunction with ultrasound speckle de-correlation analysis to determinethe position and orientation of the ultrasound probe at each moment intime. For example, Kalman filters can be used to combine the positioninginformation form the computer vision subsystem and the IMU. Fiduciaryelements can be placed on the patient or on stable objects adjacent tothe patient to give a reference frame for the virtual reality model andto provide the proper scale for the whole environment when using thecomputer vision system for registering the ultrasound probe into the 3-Dmodel. The fiduciary element can be made of a patterned layer made ofvarious colors or shades, can comprise reflective objects, or activelighting elements, such as light emitting diodes (LEDs). Likewise, thefiduciary element can be rigid, flexible, or piece-wise rigid.Additionally, a miniature light projector, light source, LED or lasercan be integrated into the system, such as into the body of the machinevision camera subsystem 104, to cast a light onto the field of view ofthe camera for better visualization.

In an alternative implementation, the fiduciary object may not be used,and in order to get calibration and scale information, the camera videostream is combined with the IMU data. In principle, it is possible todetermine the position of the probe without the use of a fiduciaryobject, by analyzing the fixed visual features in the field-of-view.Examples of such features are room edges and corners, furniture, andlights. The computer vision algorithms can analyze the apparent positionof these highlights to determine the position and orientation of thecamera, and by simple transformations, of the probe.

FIG. 10B shows an embodiment of an ultrasound transducer with a machinevision and tracking subsystems integrated into the body of the housingfor probe. The ultrasound imaging probe housing 1011 is in contact withthe investigated patient 1012 through the ultrasound probe head. Thebody of the ultrasound transducer subsystem inside the ultrasound probeis represented schematically by dashed box 1013. The ultrasoundtransducer subsystem can comprise a mechanically scanned transducer, aphased array of transducers, or a combination of these.

Electronics for signal generation, signal conditioning, data processingand read-out may be placed inside the probe housing. A board 1014accommodates all these electronics. This board can be connected to acable 1015 that makes the connection to a computing unit orvisualization device. Alternatively, the on-board electronics cancommunicate wirelessly with other computing and visualization units. AnIMU is abstractly shown connected to the on board electronics 1014 asthe dashed box 1016. A board 1017 accommodates the camera. This boardcan be electrically in contact with the board 1014. The body 1018 of thecamera and lenses is within housing 1011. A visor 1019 on the ultrasoundprobe body allows light to penetrate into the lenses of the camera.Additionally, a button 1020 on the probe housing can be used for theuser to interact with the functionalities of the system. For example, itcan be used to start and stop the system, change acquisition modes, etc.

In another embodiment, ranging systems can be used to determine thecontour of the patient and to track and spatially register theultrasound probe in respect to the patient and other instruments.

FIGS. 11A-11C show examples of ultrasound imaging probes with trackingcapability using ranging cameras mechanically registered to theultrasound probe. In these embodiments, a ranging camera as described inFIG. 1 is used. The drawings of the figures show an ultrasound probehousing 1101 in contact with an investigated patient 1102.

FIG. 11A shows a lateral sectional view of the probe housing. FIG. 11Bshows a front view of an embodiment with one ranging camera. FIG. 11Cshows a front view of an embodiment with two cameras.

Unless specified, the following descriptions apply to all three figures.The ultrasound transducer subsystem 1103 is inside the body of theprobe. The ultrasound transducer subsystem 1103 is connected toelectronics comprising signal generation, signal conditioning, dataprocessing and read-out components, also placed inside the probe housingshell. Dashed box 1104 is an abstract representation of suchelectronics. The data transfer between 1104 and a computing andvisualization units can take place wirelessly or through a cable 1105.

The ranging camera is placed in camera housing shell 1106, which can beintegrated into the ultrasound probe housing shell 1101, or can bemounted on it. In these embodiments, the housing shell comprising theranging camera and tracking elements slides into a shoe 1107 on theultrasound probe housing shell 1101 where it gets fixed with highmechanical registration. A board 1108 accommodates the ranging andtracking components. There are several components mounted on board 1108,including: a module that emits ranging signals 1109, a ranging sensor1110, and an IMU 1111. A visor 1012 on the probe housing allows rangingsignals (such as IR light) to penetrate into the lenses of the rangingcamera 1110. A generic field of view for the ranging sensor isrepresented by the angle opening 1113.

The tracking subsystem board 1108 can be connected directly to read-outelectronics or a computing unit through a cable 1114 or wirelessly.Alternatively, the board 1108 can be connected to the electronics insidethe ultrasound probe housing shell 1101 through a connector assembly1115. Whereas the cable 1116 makes the connection inside the trackingsubsystem housing shell between the board 1108 and the connector 1115,the cable 1117 makes the connection inside the ultrasound probe housingshell 1101 between the connector 1115 and the board 1104 or between theconnector 1115 and the read-out cable 1105, directly. The electricalconnection inside the connection system 1115 can be made when thetracking subsystem housing shell 1106 is slid into the shoe 1107.Additionally, a button 1118 on the probe housing shell can be used forthe user to interact with the functionalities of the system. Forexample, it can be used to start and stop the system, change acquisitionmodes, etc.

FIG. 11B shows a front view of the whole assembly showcasing a singleranging sensor. In a time of flight implementation, one or more lightsources 1109 are part of the time of flight camera, whereas the lightsensing component of the time of flight camera is behind the window1112. When a structured light implementation is used, the level armbetween the light source 1109 and the light sensor will be increased sothat appropriate ranging performance is obtained for the range ofdistances of interest.

FIG. 11C shows a front view of the whole assembly showcasing two lightsensors behind windows 1112 and 1119. In a time of flight ranging cameraimplementation, one or more light sources 1109 can be combined with twotime of flight light sensiors behind the windows 1112 and 1119. In astructured light ranging camera implementation, a structured lightsource 1109 can be combined with two light sensors behind the windows1112 and 1119 on either side of the structured light source to create astereoscopic structured light camera. This arrangement will insureoverlap in the field of view of the structured light source with thefield of view of at least one light sensor.

The ranging camera can use most preferably IR light, so that the lightsource 1109 is a IR light source, and light sensor is optimized todetect IR light. However, light or any color could be used. In a hybridimplementation that combines a ranging camera with a non-ranging camera,a ranging assembly can be made of one or more light sources 1109 and aranging sensor behind window 1112, and the sensor behind window 1119 canbe a non-ranging light sensor, such as a RGB (red green blue) orblack-and-white (B/W) CMOS or CCD. In a pure machine vision cameraimplementation, a light source 1109 can be used mainly for sceneillumination, with the sensors behind windows 1112 and 1119 forming astereoscopic camera. In this case, stereoscopic machine visionalgorithms can be used on the computing unit to analyze the data fromthe two sensors to create a dense, 3-D model of the contour of objects,and for spatial registration of the ultrasound probe in respect to theinvestigated patient.

The ranging and probe tracking embodiments, as exemplified in the figurecan also be used in conjunction with other probes, such as gamma-probesfor lymph node detection as described above and in FIG. 9 .

FIG. 12 shows various ways in which an ultrasound probe with integratedtracking capabilities as exemplified above can be coupled to read-out,data processing and visualization units.

FIG. 12A shows a read-out which more closely integrates the streams fromthe tracking subsystem and ultrasound probe. The ultrasound probeassembly 1201 is shown with two cables, one 1202 primarily forultrasound control and data read-out, and another one 1203 primarily fortracking subsystem control and data read-out. Two cables shown in thefigure, but a single cable can also be used to carry all information.The two connections 1202 and 1203 connect to an electronics module 1204comprising components for beam-forming, signal processing and datacollection. Inside module 1204 data from the tracking subsystem andultrasound probe can be time synchronized and associated with eachother. The data connection 1206 transmits primarily tracking subsystemdata between the data conditioning unit 1204 and the computing unit1205. Likewise, data connection 1207 transmits primarily ultrasoundprobe scan data between the data conditioning unit 1204 and thecomputing unit 1205. Data connections 1206 and 1207 can use the samecable or connections, or separate connections. Units 1204 and 1205 canbe physically separate, or integrated into a single device.

In some implementations, all or part of the electronics of 1204 can beintegrated into the ultrasound probe housing. In that case, theconnections 1202 and 1203 can link directly to the computing unit 1205.Examples of such a computing unit are: a computer, laptop, tablet, smartphone, or other custom processing unit. In some implementations, thecomputing unit itself can be integrated into the housing of theultrasound probe assembly 1201.

Inside the computing unit 1205, algorithms and methods can be used toprepare ultrasound data for visualization, to register the ultrasoundprobe in respect to the patient by analyzing the probe trackinginformation, to build 3-D models of the patient, to allow users tocontrol and manipulate ultrasound and tracking data, to storeinvestigation data, to retrieve previously stored data, to provideconnections with other computing units, internet or local network,servers, etc.

FIGS. 13 and 14 shows examples of such methods that can be implementedinside the computing unit.

A visualization device 1206 (see FIG. 12 ), such as a monitor, touchscreen, projector, head mounted displays, goggles or augmented realityglasses can be used to visualize and interface with the data. Theoperator of the probe can interface with the system though amouse/keyboard, touch screen, joystick of other non-contact devices,such as structured light or time of flight ranging systems thatinterpret the hand and finger movements of the operator.

FIG. 12B shows a read-out which does not closely integrate the streamsfrom the tracking subsystem and ultrasound probe. This implementation ismore suitable when the probe tracking capability and associated methodsare implemented to existing ultrasound machines. Such implementationwould allow existing ultrasound systems to be fitted with new ultrasoundprobes that have tracking capability.

The ultrasound probe assembly 1211 is shown with two cables, one 1212primarily for ultrasound control and data read-out, and another one 1213primarily for tracking subsystem control and data read-out. For existingultrasound machines, there is normally limited capability to provide aconnection for the tracking subsystem. Also, most commonly, theelectronics module 1214 for beam-forming, signal processing and datacollection and the computing unit 1215 for further processing andvisualization are integrated into a common physical body.

Many commercial ultrasound machines provide an ultrasound scan output,such as a data or video output for the visualization of ultrasound scanand controls on external monitors. This output can be read-out by asecond computing unit 1216 which also connects to the tracking subsystemthrough connection 1213. Methods for data synchronization, dataprocessing, probe registration, 3-D model formation, data storage andretrieval, user interface, communication with other servers orcomputers, and connection to networks can be implemented inside unit1216. Finally, a visualization device 1217, similar to 1206 can be usedto visualize and interface with the data.

With the present invention, we also introduce new methods for ultrasoundinvestigations, such as remote-guided ultrasound investigations,computer guided ultrasound investigations, ultrasound stereotaxy,freehand spatial compounding, tissue characterization, tissueelastometric property characterization, and enhanced freehand 3-Dultrasound. Many of these methods are made available by probe trackingtechniques as introduced here, or other tracking techniques.

FIG. 13 shows an example of how such methods can be implemented in acomputing device. The processes supporting the introduced methods can beseparated in three main blocks: tracking and volumetric modeling,ultrasound processing, and visualization and interface. As exemplifiedin the figure, modules 1301 to 1309 are part of the tracking andvolumetric modeling block, modules 1312 to 1317 are part of theultrasound processing block, and 1310, 1311, 1318, 1319, 1320 are partof the visualization and interface block.

The data from the ranging system and/or machine vision system 1301 canbe combined with the data from a tracker 1302, such as an IMU inside the1303 processing module inside the computing unit, to create ultrasoundprobe tracking information. The combined data can also be used to buildthe 3-D outline of the patient inside module 1304. Other data stored ona local storage device or from the network 1305 can be loaded to supportfunctionalities, such as expert guidance, remote guidance and ultrasoundstereotaxy. This data is loaded into a gateway module 1306.

The probe tracking information from 1303, the patient contourinformation from 1304 and other stored information from 1306 can bemerged to build a virtual reality (VR) model inside module 1307. Thismodel can comprise the contour of the patient, models of the ultrasoundprobe in respect to the patient, 3-D or sectional organ models, currentand previously stored ultrasound and other imaging models, other medicalinstruments, graphical user interface components, links to other data,and other linear, areal and volumetric components and measures. The VRmodel can be sent over the network, or locally saved in its whole orparts of it inside 1308 module. The data sent to module 1308 can beassociated with other data, such as the ultrasound data of 1314. Bykeeping track of the volumetric elements scanned by the ultrasoundsystem during an investigation, it is possible to build a 3-D modelrepresenting the volumes inside the patient that have been alreadyinvestigated, and the volumes inside the patient that may require moreinvestigation. This process is done inside module 1309. The VR model, orparts of it, can then be sent to a rendering and visualization module1310. Likewise, the 3-D model representing investigated volumes orvolumes that require more investigations is sent to a rendering andvisualization module 1311. The two models can be co-registered andsuperposed inside a unified model.

Another analysis block in the figure includes ultrasound analysisprocesses. The ultrasound data stream coming from the ultrasound proberead-out 1312 is synchronized and associated with the probe trackingdata stream so that the probe tracking information is appended to theultrasound data bunches inside module 1313. The ensuing time- andposition-registered ultrasound stream, which will be called a “spatiallyregistered scan,” can be sent over the network or saved locally on astorage device 1314. The VR model in its entirety or parts of it can beappended to the ultrasound data saved on the local storage device orsent over the network to another location. The ultrasound data can beanalyzed to create 2-D scans, such as B-scans, elastography map, Dopplerflow or other tissue characterization maps inside module 1316. Thespatially registered ultrasound scans can be analyzed using spatialcompounding methods to not only filter out ultrasound speckle andartifacts, but also to extract more accurate information about types oftissues inside module 1317. This can be done by analyzing multiplespatially registered scans that cover the same area from differentultrasound transducer positions and angles. In the present context, thisspatial compounding analysis can be referred to as a limited scope 3-Dfreehand ultrasound.

The 2-D scans delivered by 1316 can then be visualized inside thevisualization and interface module 1318. Likewise, the spatiallycompounded model or tissue type model delivered by 1317 can bevisualized by module 1319. At each moment in time, the spatiallycompounded model to be visualized will be updated repeatedly to includethe data from the latest spatially registered scans. For example, in oneimplementation, the user can observe on a visualization device thesection of the compounded model or tissue type model that corresponds tothe section being scanned at that moment by the ultrasound probe. Inthis way, the user can easily navigate the spatially compounded model ortissue type model by moving the ultrasound probe on the patient.Controls can be provided to the user to adjust visualization andprocessing settings for the tissue characterization maps. The mapsvisualized by modules 1318 and 1319 can also be merged into a commonvisualization module.

By using most of the spatially registered ultrasound scans collectedduring an investigation, a full 3-D model can be created. This can bereferred to as “freehand 3-D ultrasound imaging.” This process isindicated in module 1315. The data can come from a local storage device,from the network, or directly from a memory. The process can take placeoff-line, but if computing resources are available, it can also takeplace in real-time. The output model can be saved on a local storagedevice, sent over the network, or sent to a visualization module 1320optimized to visualize 3-D models, including tissue type, elastometricproperty, flow, or to the more generic VR visualization module 1310.

FIG. 14 gives an example of how some of the above methods can beintegrated into a telemedicine and operator guidance system. The localsystem 1401 is the system setup at the place where the patient istreated or evaluated by the “local” clinician. The remote system 1402 isthe system setup at the site of the “expert” remote clinician. Theexchange of data is done through a communication network 1403. This canbe, for example, an Internet network, a local computer network, or awireless network. The Computer Vision System 1404 may provide 3-Dmodels, such as patient 3-D contour, as well as probe trackinginformation.

The tracking information from 1404, if available, is combined with thetracking information delivered by the inertial measurement unit system1405. A 3-D virtual modeler system 1406 merges the information from 1404and 1405 into a combined 3-D model. This model is send over thecommunication network 1403 to the remote system 1402, where it iscombined with tracking information provided by the remote trackingsystem 1407. The core purpose of the remote tracking system 1407 is toallow the remote clinician to communicate to the local clinician his orher choice in what regards the manipulation of a medical device, such asan ultrasound imaging probe. The data streamed out of 1407 will comprisethe position and orientation of the probe, as elected by the remoteclinician.

To create this stream of data, the remote user should have an intuitiveway to do it. A machine vision system combined with an IMU trackingsystem similar to the setup at the “local” site will most probably bethe most intuitive way. Using this implementation, the “remote” userwill just have to move a mock-up medical instrument at the remote sitein a similar fashion as the local clinician. For direct feed-back to theremote user, a combined 3-D virtual reality modeler and movementguidance system 1408 will include the position of the medical instrumentproposed by the remote user into a common 3-D model. The position of themedical instrument proposed by the remote user delivered by 1407 will besent over the network to the local system to be combined with the 3-Dvirtual model within the a combined 3-D virtual reality modeler andmovement guidance system 1409, which is basically a mirror of the remotesystem 1408.

However, whereas the purpose of 1408 is to create feed-back to theremote user in what regards her/his proposed position of the medicalinstrument in respect to the 3-D model, the purpose of 1409 is to createinformation for the local operator she or he can use for guidance in howto manipulate the medical instrument. The stream of data coming from themedical instrument 1410 will be visualized locally by the local operatorusing a visualization system 1411. The combined 3-D model coming from1409 will be visualized as well, preferably on the same device 1411. Theremote user will monitor the visualization system 1412 to inspect thedata taken by the medical instrument 1410, and to get feed-back on heror his manipulation of the probe mock-up that is part of the remotetracking system 1407. The visualization systems 1411 and 1412 can bescreens, or augmented reality systems worn by operators or users.

The remote tracking system can utilize a similar tracking system as thelocal tracking system, or it can be implemented in several other ways.Examples are: a joystick, a computer mouse, a keyboard, a rangingdevice, or other human interfaces.

For the case when the medical instrument is an ultrasound scanner, anexample of visualization and graphical user interface screen is shown inFIG. 15 . The visualization area 1501 may comprise one or more windowsand panels. In a more general implementation, the visualization areawill comprise a panel 1502 containing buttons and links to settings andcontrols for the ultrasound system, computer vision system, IMU,visualization, data processing modules, etc. The ultrasound image 1503may represent a regular B-scan, or a more advanced imaging output, suchas a tissue type weighted image, fluid flow, tissue movement, tissuetype, tissue elastometric properties, or a combination of any of these.The window 1504 shows a 3-D representation of the 3-D virtual model ofthe setup. Other windows can show footage of the computer vision orranging camera in window 1505, and other data in window 1506, such asvideo image from the remote site, or processed ultrasound data, such as:

3-D or 2-D sections of a model of patient that can include modelsimported from other imaging modalities, such as computed tomography(CT), magnetic resonance imagin (MRI), positron emission tomography(PET), or single-photon emission computed tomography (SPECT);

3-D of 2-D tissue weighted images (tissue characterization and fluidflow);

representation of 3-D organ segmentation;

anomaly detection result;

volumetric rendering of volume that has been scanned;

volumetric rendering of volume that requires more scanning;

any section of any of these models of combination of them.

The window 1504 comprising the 3-D model of the patient can alsocomprise any of the elements described for window 1506, as well as 2-Dultrasound scans. The purpose of this window can be to guide the localclinician on the best position and orientation of the probe in respectthe patient 1507. The best position and orientation of the probe issuggested either by the local analysis results, as indicated by acomputer system, or as recommended by a remote user.

In window 1504, the 3-D model ultrasound probe 1508, is shown positionedin respect to the 3-D model of the patient 1507, as obtained by thetracking system. The recommended position of the probe is represented bythe graphical guiding element 1509. The recommendation can be given byan automatic computer system, or by a remote user, as described in FIG.3 . To guide the local operator in how the probe 1508 must be moved,other visual and numeric elements can be shown, such as curved 1510 anddirectional arrows 1511, representing the rotation and translation theprobe has to make to overlap the position of the virtual probe 1509. Thegeometrical appearance of these elements, such as the length and thewidth of the arrows 1510 and 1511, can give fast feed-back to the localoperator on how large the movement of the probe must be until itoverlaps the virtual probe 1509. Additionally, or alternatively,numerical values, such as amplitude of angles (in degrees) and measuresof distances (in millimeters), each, in all three directions, can beoverlapped to give the local operator information about movement of theprobe must be until it overlaps the virtual probe 1509. A color code canbe used to represent each of the three spatial directions fortranslations and each of the three angles for rotations, whether shownas numbers or geometric elements, such as the arrows 1510 and 1511.

Alternatively to using a monitor for visualization, an augmented realitysystem can be employed, so that the local operator can observe anoverlay of relevant elements over a direct view of the clinical set-up.Examples of elements that can be overlaid are: models of medicalinstruments, such as the virtual probe 1509; numerical and graphicalindicators, such as directional arrows 1510 and 1511; 3-D anatomicalmodels; ultrasound images and models, and others.

One disadvantage of tele-guided ultrasound functionality is that ahighly trained expert is still required to be available for theinvestigation. An alternative to that is to have a local computerguidance system that has preloaded procedures for a large array ofclinical investigations. The patient contour as measured by the rangingor light sensing system can be matched to the outline of a generic humanmodel. This will allow the computer guidance system to give preciseinstructions about the positioning and movement of the ultrasound probein respect to the real patient model. Ultrasound anatomical landmarksobserved in real-time can be matched in 3-D to landmarks in the 3-Dmodels for a much more precise registration that will correct for organmovements and displacements due to variations in body habitus andposition. An ultrasound image interpretation can be given by the localuser, expert system, or later by a radiologist.

A “stereotactic ultrasound” instrument as described herein can allow theuser to label features of interest in 3-D, and register them withrespect to the patient model so that follow-up investigations can easilyuse those coordinates to re-evaluate medical conditions. The user can begiven software tools to mark features in the 2-D ultrasound scan. Sincethe ultrasound probe position will be spatially registered to the 3-Dmodel of the patient contour, the marked structure will be registeredwithin the 3-D patient model. Moreover, the positioning of theultrasound probe with respect to the body can be retained so that it canbe reproduced by an operator at a later moment. Similarly to thecomputer guided ultrasound functionality explained above, ultrasoundanatomical landmarks observed in real-time can be matched in 3-D toultrasound landmarks previously stored during previous examinations, orto other 3-D models, for a much more precise registration that willcorrect for organ movements and displacements. Tools for volumesegmentation and measurement can be used to quantitatively evaluatevarious conditions and to track changes in time.

An advantage of the ultrasound system, as exemplified above, is that itcan be used very efficiently as a “freehand” 3-D ultrasound system. A“freehand ultrasound” uses a regular 2-D ultrasound probe as theoperator moves it across the body of the patient. Combining successive2-D ultrasound images, a 3-D model of the whole investigated volume isformed. Since a whole 3-D model will be created by keeping track of all2-D scans, the final result of the investigation will be practicallyindependent on the skill of the operator to take relevant ultrasoundcross-sections, and to notice relevant features.

A tracking system, as described above, can make freehand 3-D imagingfunctionality possible in an inexpensive, operationally efficient way.Various 3-D ultrasound models, such a tissue type weighted image, fluidflow, tissue movement, tissue elastometry properties can be obtained byusing the freehand ultrasound capability of the system. Moreover, areal-time 3-D modeling of the patient layout will help the freehandultrasound imaging process by providing information about changes in thepatient position and skin layout. These changes can occur, for example,because of forces applied on the patient skin, such as by the ultrasoundprobe, voluntary of involuntary changes in the patient position, andbecause of patient breathing. This capability will help prediction oforgan movement, improving the quality of the 3-D ultrasound modeling.

Tracking methods and systems that use at least a camera or rangingdevice to track the relative position of instruments, sensor probes,objects or parts of a user in respect to each other, or in respect tothe at least one camera or ranging device are proposed. The at least onecamera or ranging device can be positioned in such a way as to observethe general area where instruments, sensor probes or objects of interestor being acted upon by the user are positioned. As such, the at leastone camera or ranging device can be positioned on a mount or on anobject adjacent to the general work area, or can be carried by a humanor robotic user. Examples of the at least one camera or ranging devicesare: visual color camera, visual B/W camera, IR camera, plenopticcamera, time-of-flight camera, stereoscopic camera, structured lightcamera, stereoscopic structured light camera, ultrasound trackers, orelectromagnetic trackers, such as magnetic trackers or radio-frequencytrackers.

A computing unit can be operatively coupled with a memory and the atleast one camera or ranging device, the memory having instructions forexecution by the at least one processor configured to determine aspatial position and orientation of the instruments, sensor probes,objects or parts of a user in respect to each other, or in respect tothe camera. For better tracking capability, fiducial markers or objectscan be mounted on instruments, sensor probes or objects of interest tobetter determine their position and orientation. Examples of fiducialmarkers are reflective objects, objects with distinct shapes, binaryblack and white or colored coded tags with distinct codes. To increasethe effective field of view for the objects of interest, instruments orsensor probes, more than one fiducial element can be mounted or attachedto each of these. For example, a cube like element can comprise tags oneach of its surfaces, so that at least one tag can be seen from anyangle by the at least one camera or ranging device.

In the case when the at least one camera or ranging device is anultrasound tracker, ultrasound detectors mechanically registered to theobjects, instruments or sensor probes will be used. In the case when theat least one camera or ranging device is an electromagnetic tracker,electromagnetic sensors mechanically registered to the objects,instruments or sensor probes will be used.

Tracking the location and orientation of instruments, sensor probes andinvestigated objects in respect to the at least one camera or rangingsystem is done using the methods described earlier in this invention.However, of relevance is mainly the relative location and orientationbetween instruments, sensor probes and investigated objects. This isachieved by transformations taking into account the position andorientation of each element in respect to the at least one camera orranging system.

A computing unit can be operatively coupled with a memory and the atleast one camera or ranging device, the memory having instructions forexecution by the at least one processor configured to create a 3-D modelof the setup, including a contour of the objects of interest,instruments, or sensor probes.

At least one processor can be operatively coupled with a memory and theat least one camera or ranging device, the memory having instructionsfor execution by the at least one processor configured to observe andanalyze movements of interactivity elements, such as parts of user'sbody or other objects, interpreting those movements to activate aprocess inside the at least one processor. Examples of interactivityelements can be: fingers, arms, instruments, pens, sticks, styluses. Inorder for the user to properly interact with the computer by movinginteractivity elements, a display operationally coupled to the at leastone processor will show the position of these interactivity elements inrespect to a graphical user interface element, virtually positioned inthe same general space as the interactivity elements. The user will begiven regular computer interactivity tools such as: click, scroll,navigate files, models or images, zoom-in, zoom-out, type, etc. Thedisplay can be a computer monitor, an augmented reality system, and ahead-mounted display.

In one implementation, the at least one camera or ranging system can bepart of a head-mounted tracking and visualization (HMTV) system. ThisHMTV system can comprise not only tracking and ranging components, butalso a display that allows the user to see images of interest, VRmodels, graphical interfaces, an augmented reality model, or otherelements of interest. In one implementation, the user can use objects,or parts of his or her body to interact with the computer by moving themin the field of view of the at least one camera or ranging system. Forbetter tracking capability, and potentially for better interactivitywith the computer, the HMTV can also comprise an IMU. For example, withthe help of the IMU, or the head-mounted at least one camera or rangingdevice, or a combination of these, the user could employ head gesturesto execute a process on the at least one processor.

FIG. 16 shows an example of an implementation where the at least onecamera or ranging device is mounted on a HMTV system. For clarity, onlyone sensor probe is shown in this figure. A user 1600, such as aphysician, investigates a object of interest 1601, such as a patient,using a sensor probe 1602, such as an ultrasound probe. The user wear ahead mounted tracking and visualization system (HMTV) 1603, whichcomprises a camera system made out of two light sensing devices 1604 and1605 and a light emitter 1606, which can be part of a structured lightcamera, a time of flight camera, a LIDAR sensing camera, or a flashLIDAR camera. More cameras could be used. This camera system cancomprise a time of flight camera and a non-time-of-flight camera, astereoscopic structured light system, a single camera structured lightsystem and a visual camera, or any other combination. In this particularimplementation the display 1607 is part of the HMTV system.Alternativally, or additionally, an external display can be used. Thedisplay 1607 can be a semitransparent display, can be an opaque display,or can be designed to only cover a part of the user's visual field ofview. A representation of an image that could be shown by the display1607 is shown inside the rectangle 1608.

The sensor probe 1602 carries a fiducial object 1609, mechanicallyregistered to it, in the shape of a cube, on the surface of whichdistinct binary fiduciary tags are shown. In this figure, only two tagsare visible: 1610 and 1611. This fiducial object can be part of the samehousing shell as the sensor probe, can be part of a housing shell thatmounts to the sensor probe housing shell in a similar fashion as camerahousing shell 1004 or 1106, or can be mounted with a bracket on thesensor probe housing shell. In another implementation, both a fiducialobject and a camera can be mechanically registered to the sensor probeor instrument. In another implementation, camera housing shells, such as1004 or 1106) can be interchangeable with the fiducial object 1609.Another fiducial object 1612 in the form of a piece-wise rigid fiducialwith distinct binary coding can be laid down or fixed to theinvestigated object 1601. The user 1600 can use his or her fingers 1613as interactivity elements to interact with the computer (not shown). Inone implementation, the computer could be carried by the user. Inanother implementation, the computer can be partially contained by theHMTV housing. In yet another implementation the computer can be placedinside the sensor probe housing 1602.

Buttons B1, B2, B3, B4, B5 showed by the display represent genericgraphical user interface a user can virtually touch with interactivityelements 1613 to execute a process on the computer. For clarity, onlybutton B4 is labeled by reference numeral 1614. The display 1607 alsoshows a 3-D virtual model 1615 or stereoscopic view of the setup, as itcould be created by the camera system on the HMTV 1603, by itself, or incombination with other cameras or ranging systems mechanicallyregistered to instruments or sensor probes, or mounted on other externalobjects. The purpose of this window can be also for computer and remoteguidance as explained above. Window 1616 shows a scan delivered by theimaging sensor probe, in this case, this is an ultrasound scan.

Additionally, another tracking system, such as an IMU, can bemechanically registered to the HMTV or to the instrument and sensorprobes for improved tracking performance, and for supplementary userinteractivity with the computer.

When the sensor probe is an ultrasound transducer, many previousinvestigative modalities explained above can be used in thisimplementation. Correspondingly, this implementation can allow forremote and computer guidance, ultrasound stereotaxy, freehand spatialcompounding, freehand tissue elastometry, freehand 3-D imaging, tissuecharacterization, as well as other applications, such as needle guidanceusing ultrasound, ultrasound assisted surgery, etc.

When the sensor is a gamma-ray probe, this implementation will allow thesurgeon to visualize directly on the display the 3-D distribution of theradioactive tracer with respect to the body outline.

Stereotaxy, computer and remote guidance uses can also be found when theinstrument or sensor probe is any of the following: hand-held imagingdevice, surgical instruments, laparoscopic instruments, etc.

Many other intraoperative uses of the presented methods andimplementations can be found. These examples are non-limiting and showhow the methods disclosed in this invention can be implemented inpractice.

Alternative Modes

Another field where aspects of this invention can provide significantadvantages is in environmental surveys. Spatial registration systemsattached to surveying sensors can be used to automatically performenvironmental surveys. The spatial registration system will convenientlyprovide the position and orientation of the system in relationship tothe investigated objects or to the adjacent environmental objects,keeping an automatic log of the surveyed locations. This capability willalso allow for an automatic mapping of the investigated features.

One particular example of an application that will benefit from such acapability is the measurement of the radioactive dose or radiation fieldinside structures. In such an application, among other sensors, any ofthe following sensors can be used: a radiation dosimeter, aspectroscopic detector, a radiation imaging system, a spectroscopicimaging system. Likewise, this capability can be used to map a chemicalfield using chemical or biological sensors.

FIGS. 17A-17C illustrate a probe, such as a dosimeter, radiationdetector or chemical sensor, attached to a smart phone in accordancewith an embodiment. Here, a portable computer or a smart phone 1701 canbe used for computer vision processing, for data visualization using itsbuilt-in screen 1702 and for video image capture using the built-incamera 1706. Where available, an extra built-in video camera 1707 can beused for stereoscopic implementations. A sensor probe 1703 is clipped onto the smart phone device 1701 with good mechanical registration througharm 1705 and connector body 1704.

Examples of probe sensors 1703 can be radiation detection devices,radiation dosimeters, radiation imagers, spectroscopic radiationimagers, chemical sensors, bio-chemical sensors, infra-red sensors, etc.

A software program on the smart phone or the equivalent portablecomputer can be used to acquire the data from the built-in video camerasand from the sensor probe. Furthermore, the program can contain thenecessary computer vision algorithms to provide spatial registration andtracking of the sensors in respect to the investigated environment andobjects. Having this, a field map of the investigated environment can beobtained. For example, if a radiation dosimeter is used as a sensorprobe, a map of the radiation dose field is obtained. The map can be 1D,2D or even 3D, as demanded by the application. Where the localprocessing power allows it, the processing can be done completely onboard. Where local processing power is not sufficient to accommodate allsoftware needs, raw or partially analyzed data can be sent wirelessly orthrough wires to another external processing unit.

FIGS. 18A-18C show a hand-held probe with an integrated spatialregistration system in accordance with an embodiment. Here, a dedicatedhand-held device contains the spatial self-registration system body1801, a body 1802 that comprises the sensor probe, data acquisition andprocessing unit (computer), and a handle 1804 that may comprise battery,voltage supply, or other sensors. A screen 1803 may be integrated forvisualization and user interfacing. The spatial self-registration systemmay comprise one or more cameras 1805 and 1806, a laser beam source1807, a sensor 1808 to detect reflected laser light. The laser beamassembly made of 1807 and 1808 can be used for laser ranging (lidar),for time of flight ranging, or for structured light ranging in order toobtain supplementary range information about the scene.

The data acquisition and analysis software can be implemented on boardof the hand held device on the processing unit. Likewise, the algorithmsfor spatial self-registration can be implemented on board.Alternatively, the data can be sent wirelessly or through wires to otherexternal processing units. As explained above, such system may alsoinclude an INU and a GPS sensor.

FIG. 19 illustrates a representation of the way the device shown in FIG.7 can be used in practice. In a survey scenario, the user 1901 will holdthe survey system 1902, such as a chemical sensor or a radiationdosimeter, that has self-registration capability (similarly to thedevice shown in FIG. 18 ) to scan the field but also to acquireinformation about the relative position of the sensor in theenvironment. The system 1902 may contain a lidar ranging system thatpoints a laser beam 1903 to the adjacent objects. The video camera(s)integrated into the system 1902 may have a field of view represented bythe lines 1904. A computer vision algorithm can be used to identify thelaser spot in the visual picture allowing a match of the rangeinformation from the lidar with the features seen by the computer visioncamera. This will allow absolute scaling of the 3D model delivered bythe computer vision system.

While the invention has been described by way of example and in terms ofthe specific embodiments, it is to be understood that the invention isnot limited to the disclosed embodiments. To the contrary, it isintended to cover various modifications and similar arrangements aswould be apparent to those skilled in the art. Therefore, the scope ofthe appended claims should be accorded the broadest interpretation so asto encompass all such modifications and similar arrangements.

What is claimed is:
 1. A spatial registration apparatus comprising: agamma ray detector; a ranging sensor rigidly connected with the gammaray detector, wherein the ranging sensor is selected from a groupconsisting of an optical camera, a stereoscopic imaging camera, aninfrared camera, a scanning laser camera, a flash laser camera, atime-of-flight camera, a structured light camera, and an electromagneticsensor; and at least one processor operatively coupled with a memory,the memory having instructions for execution by the at least oneprocessor, wherein the memory stores a relative location and orientationbetween the gamma ray detector and the rigidly connected ranging sensor,wherein the instructions, when executed by the at least one processor,cause the at least one processor to capture distance values to selectedpoints on a surface of an object scanned by the ranging sensor, create athree-dimensional (3D) model of the surface using the distance values,determine a pose of the ranging sensor with respect to the 3D model ofthe surface of the object, and then transform the pose, using the storedrelative location and orientation between the gamma ray detector and therigidly connected ranging sensor, to determine a first spatial positionand orientation of the gamma ray detector with respect to the 3D modelof the surface of the object, the at least one processor associatingscanning data from the gamma ray detector with the first spatialposition and orientation of the gamma ray detector to create a firstspatially registered scan, the scanning data from the gamma ray detectorbeing time synchronized with the first spatial position and orientationof the gamma ray detector.
 2. The apparatus of claim 1, wherein thegamma ray detector includes a Compton imager or a collimator basedimager.
 3. The apparatus of claim 1, wherein the gamma ray detectorincludes a gamma ray probe that includes a semiconductor detector or ascintillator.
 4. The apparatus of claim 1, wherein the instructions forexecution by the at least one processor further cause the processor toconstruct a two-dimensional (2D) or a 3D model of a radioactive tracerwith respect to the object using the first spatially registered scan. 5.The apparatus of claim 4, wherein the instructions for execution by theat least one processor further cause the processor to render, on adisplay, the 2D or 3D model of the radioactive tracer.
 6. The apparatusof claim 1, wherein the object includes a body of a patient, theinstructions for execution by the at least one processor further causethe processor to guide a human or robotic operator to move a medicalinstrument to a particular point on or within the patient's body usingthe 3D model of the surface of the object.
 7. A spatial registrationapparatus comprising: a gamma ray detector; a ranging sensor rigidlyconnected with the gamma ray detector, wherein the ranging sensor isselected from a group consisting of an optical camera, a stereoscopicimaging camera, an infrared camera, a scanning laser camera, a flashlaser camera, a time-of-flight camera, a structured light camera, and anelectromagnetic sensor; and at least one processor operatively coupledwith a memory, the memory having instructions for execution by the atleast one processor, wherein the memory stores a relative location andorientation between the gamma ray detector and the rigidly connectedranging sensor, wherein the instructions, when executed by the at leastone processor, cause the at least one processor to capture distancevalues to selected points on a surface of an object scanned by theranging sensor, determine a pose of the ranging sensor with respect toselected points on the surface of the object, and then transform thepose, using the stored relative location and orientation between thegamma ray detector and the rigidly connected ranging sensor, todetermine a first spatial position and orientation of the gamma raydetector with respect to the selected points on the surface of theobject, the at least one processor associating scanning data from thegamma ray detector with the first spatial position and orientation ofthe gamma ray detector to create a first spatially registered scan, thescanning data from the gamma ray detector being time synchronized withthe first spatial position and orientation of the gamma ray detector. 8.The apparatus of claim 7, wherein the gamma ray detector includes aCompton imager or a collimator based imager.
 9. The apparatus of claim7, wherein the gamma ray detector includes a gamma ray probe thatincludes a semiconductor detector or a scintillator.
 10. The apparatusof claim 7, wherein the instructions for execution by the at least oneprocessor further cause the processor to construct a two-dimensional(2D) or a three-dimensional (3D) model of a radioactive tracer withrespect to the object using the first spatially registered scan.
 11. Theapparatus of claim 10, wherein the instructions for execution by the atleast one processor further cause the processor to render, on a display,the 2D or 3D model of the radioactive tracer.
 12. A spatial registrationapparatus comprising: a gamma ray detector; a camera rigidly connectedwith the gamma ray detector, wherein the camera is selected from a groupconsisting of an optical camera, a stereoscopic imaging camera, aninfrared camera, a scanning laser camera, a flash laser camera, atime-of-flight camera, and a structured light camera; and at least oneprocessor operatively coupled with a memory, the memory havinginstructions for execution by the at least one processor, wherein thememory stores a relative location and orientation between the gamma raydetector and the rigidly connected camera, wherein the instructions,when executed by the at least one processor, cause the at least oneprocessor to create a three-dimensional (3D) model of a surface of anobject scanned by the camera by using at least two camera frames takenwith the camera at different locations, determine a pose of the camerawith respect to the 3D model of the surface of the object, and thentransform the pose, using the stored relative location and orientationbetween the gamma ray detector and the rigidly connected camera, todetermine a first spatial position and orientation of the gamma raydetector with respect to the 3D model of the surface of the object, theat least one processor associating scanning data from the gamma raydetector with the first spatial position and orientation of the gammaray detector to create a first spatially registered scan, the scanningdata from the gamma ray detector being time synchronized with the firstspatial position and orientation of the gamma ray detector.
 13. Theapparatus of claim 12, wherein the instructions for execution by the atleast one processor further cause the processor to construct atwo-dimensional (2D) or a 3D model of a radioactive tracer with respectto the object using the first spatially registered scan.
 14. Theapparatus of claim 13, wherein the instructions for execution by the atleast one processor further cause the processor to render, on a display,the 2D or 3D model of the radioactive tracer.
 15. The apparatus of claim12, wherein the object includes a body of a patient, the instructionsfor execution by the at least one processor further cause the processorto guide a human or robotic operator to move a medical instrument to aparticular point on or within the patient's body using the 3D model ofthe surface of the object.
 16. A method for viewing a radioactive tracerwithin tissue of a subject, the method comprising: placing a gamma raydetector and a ranging sensor over a subject, the ranging sensor rigidlyconnected with the gamma ray detector, wherein the ranging sensor isselected from a group consisting of an optical camera, a stereoscopicimaging camera, an infrared camera, a scanning laser camera, a flashlaser camera, a time-of-flight camera, a structured light camera, and anelectromagnetic sensor; acquiring scanning data of a radioactive tracerwithin the subject from the gamma ray detector; scanning the subjectwith the ranging sensor while acquiring the scanning data; determining apose of the ranging sensor with respect to the subject; obtaining astored relative location and orientation between the gamma ray detectorand the rigidly connected ranging sensor; transforming the pose usingthe relative location and orientation to determine a first spatialposition and orientation of the gamma ray detector with respect to thesubject; associating the first spatial position and orientation of thegamma ray detector with the scanning data from the gamma ray detector tocreate a first spatially registered scan, the scanning data from thegamma ray detector being time synchronized with the first spatialposition and orientation of the gamma ray detector; building atwo-dimensional (2D) or a three-dimensional (3D) model of theradioactive tracer using the first spatially registered scan; andderiving visualization data from the 2D or 3D model.
 17. The method ofclaim 16, further comprising displaying the 2D or 3D model of theradioactive tracer with respect to an outline of a body of the subject.18. The apparatus of claim 12, wherein causing the at least oneprocessor to create a 3D model of the surface of the object scanned bythe camera comprises causing the at least one processor to create a 3Dmodel of a surface of a body of a patient scanned by the camera.